When our dog was diagnosed as a diabetic, he was only 10, almost 11 years old. We spent lots of money on lab work to monitor his blood sugars, when he went into a diabetic ketoacidosis, we spent lots of money on an overnight stay, IV hydration, round the clock care, etc. They told me how much it would cost, and I wrote the check.
However within a month, he went blind and one of his eyes had a cataract that bulged through causing the eye to become necrotic. He couldn't find his way around the house, he was becoming incontinent, and was basically a vegetable. And who knows if he was in any pain from the eye, animals are very stoic! No amount of money was going to improve his quality of life and we put him down.

It was the hardest thing I've ever had to do.
I think each animal's circumstances are unique. Only you know what is the right thing to do.
Lots of times we put off the inevitable, and I can certainly understand why.
